The molecular mechanisms controlling neuroendocrine processes are studied. Special emphasis is given to the adrenergic-adenosine 3', 5'-monophosphate regulation of pineal N-acetyltransferase activity. This enzyme controls large changes in the production of the pineal product, melatonin. The effects of physiological variables on the development and function of this enzyme are investigated. These include environmental temperature, stress, and hormones. In addition, the effects of antidepressants and sympathomimetic drugs are studied. Another area of interest is circadian rhythms. The large circadian rhythm in pineal N-acetyltransferase is analyzed as to the factors and central neural structures which control this rhythm.